Am^  jour.  Pharm.  \  Improved  Deniges  Test.  637 
In  carrying  out  the  qualitative  test  it  is  essential  not  to  be 
misled  by  any  colors  developing  in  less  than  10  min.  Concentrated 
sufluric  acid  often  becomes  decidedly  weak  in  the  ordinary  labora- 
tory reagent  bottle,  and  a  transitory  color  from  acetaldehyde  may 
accordingly  appear.  This  is  also  likely  to  happen  if  the  SchifT- 
Elvove  reagent  is  not  mixed  with  the  solution  immediately  after 
addition.  The  color  arising  from  acetaldehyde  will  have  disap- 
peared in  10  min.  after  mixing,  but,  needless  to  say,  it  is  a  safe- 
guard against  error  to  run  a  blank  along  with  the  test.  On  longer 
standing,  the  test  can  naturally  detect  smaller  proportions  than  0.2 
per  cent. 
PURIFICATION  OF  SAMPLES. 
The  directions  given  for  both  quantitative  and  qualitative  work 
specify  that  the  original  material  must  be  "purified  as  necessary." 
In  general,  the  test  must  never  be  run  directly  on  any  material  un- 
less it  is  positively  known  to  contain  only  water,  alcohol,  and  other 
substances  known  to  be  innocuous.  Alcoholic  preparations  vary  so 
widely  that  no  entirely  general  methods  of  purification  may  be 
given.  The  analyst  can  generally  determine  approximately  the  na- 
ture and  amount  of  the  non-alcoholic  constituents,  and  must  decide 
whether,  in  addition  to  purification,  it  will  be  necessary  to  run  a 
blank  on  a  synthetic  mixture. 
Carbohydrates  and  Glycerol — These  substances,  against  which 
Salkowski10  has  given  warning,  are  to  be  separated  by  distillation; 
a  step  which  is  also  necessary  to  permit  determination  of  total 
alcohol  via  specific  gravity. 
Formic  and  Acetic  Acids — These  acids  are  stated  by  Rosen- 
thaler11  to  yield  color  with  SchifFs  reagent.  They  can  be  separated, 
if  necessary,  by  distillation  after  neutralization,  but  the  present 
writer  did  not  find  that  10  per  cent,  by  volume  of  either  acid  added 
to  pure  ethyl  alcohol  produced  any  color  by  the  qualitative  test. 
Formaldehyde,  Ter penes,  Etc. — These  impurities  are  removed 
by  von  Fellenberg12  by  treatment  with  sodium  hydroxide  and  silver 
nitrate,  followed  by  distillation. 
10  Z.  Nahr.-Genussm.,  28  ( 1914) ,  225. 
11  "Der  Nachweis  organischer  Verbindungen,"  1914. 
nBiochem.  Z.,  85  (1918),  45. 
